The present invention relates generally to drill guide apparatus for bone drilling tools and more specifically to an improved ratchet mechanism for bone drilling tools.
When a ligament, such as an anterior cruciate ligament (ACL) of a knee is damaged or torn, a replacement ligament is often installed in the knee to reconstruct the natural anterior cruciate ligament. During such reconstruction, a tunnel is drilled through the anterior portion of the tibia upwardly through the tibia plateau and into the distal end of the femur to approximate the natural position of the anterior cruciate ligament. A bone-ligament-bone graft is then harvested from the patellar tendon following standard procedures. Typically, a rectangular in length and trapezoid in cross-section shaped graph is cut and contoured using a graft sizer. Sutural holes are then drilled in the graft. The graft is then installed in the drilled tunnel.
The prior art includes different types of drill guides for locating tunnels in the femur and tibia for aligning and installing transverse pins to anchor the ligament replacement. One such drill guide is illustrated in U.S. Pat. No. 5,354,300. The locking mechanism for the drill guide shown therein includes a spring cog having a knife edge on the interior of a bore engaging the teeth on the drill guide movable within the bore. Although this particular mechanism works very well, it is expensive to make the knife edge in the interior of the bore. Also, since the knife edge is linear, angular orientation of this edge is important to the efficient operation of the locking mechanism. Although the knife edge may provide a substantially point contact to the teeth of the drill guide, this point contact will wear and is not adjustable to provide a fresh point contact edge.
Other types of tibial end femoral drill guides are available, for example, Restore ACL Instrument System from DePuy of Warsaw, Ind. This requires two hands to operate, one to push the drill guide and the other to operate the latch which is a cam operated or friction lock structure.
Thus, it is an object of the present invention to provide a adjustable drill guide operable with one hand and at a reduced expense.
Another object of the present invention is to provide a drill guide operable with one hand and a less complicated locking mechanism.
A still further object of the present invention is to provide a locking mechanism for an adjustable drill guide having a renewable contact surface.
These and other objects are achieved by providing at least a first arm slidable within a bore of the body of the drill guide and a ratchet mechanism for locking the first arm and the first bore. The ratchet mechanism includes teeth on the first arm and a pawl biased along a first axis and having a continuous engagement edge for engaging the teeth of the first arm for any angular orientation of the pawl about the first axis. The continuous engagement edge is a curve in a plane transverse to the first axis for providing a substantially renewable point contact with the teeth. The recess includes side walls tapered towards the engagement edge to allow a narrow contact at the engagement edge and re-enforce face walls to absorb the axial forces of the guide.
The pawl is a cylinder with a recess in a first end of a first diameter forming the engagement edge. The pawl includes a head at the second end of a second diameter greater than the first diameter. The body includes a second bore having a first and second portions of third and fourth diameters greater than the first and second diameters and joined by a shoulder. The difference between the third and fourth and the first and second diameters is sufficient to allow the pawl to cant transverse to the biasing axis of the pawl.
The first arm rotates in the first bore and includes teeth only of a portion of its transverse periphery. This allows the first arm to be retracted by rotating into the non-tooth side. The first arm is preferably hollow for receiving the drill. A second arm with the same locking arrangement may also be provided. Depending upon the specific instrument used, the first and second arms are either transverse to each other or are co-linear.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.